Wireless signaling function, e.g., function to transmit and/or receive wireless (e.g., RF, radio-frequency) signals via antenna(s), has become popular, or even essential, for modern electronic devices, such as mobile phones, smart phones, tablet/handheld/portable computers, digital cameras, camcorder, media players, game consoles, wireless network peripherals (terminals, hubs, routers), printers, navigators, wearable gadgets, etc. For efficient use of wireless signaling power, an antenna is equipped with a matching circuit (matching network), so as to match impedance of the antenna, and hence reduce reflection (return loss) due to impedance mismatch.
Modern wireless standard requires wireless signaling to be carried out at multiple bands distributed over a wide frequency range. For example, to support LTE (Long Term Evolution) telecommunication standard, wireless signaling not only needs to be implemented at conventional bands of 2G and 3G standards, but also at additional bands such as 700 MHz to 821 MHz and 2300 MHz to 2690 MHz. However, supporting bands over such broad frequency range is difficult to fulfill by traditional antenna design methodology.
Antenna design is also challenged by demand of compact antenna dimensions. Size (e.g., width, length and/or area) of antenna is expected to be small due to the following reasons. For extensive interconnectivity, modern electronic device needs to include supports for multiple wireless standards, such as mobile telecommunication (2G/3G/LTE), NFC (Near-Field Communication), GPS (Global Positioning System), Bluetooth, and/or Wi-Fi, etc. Since electronic device has to include different antennas for different wireless standards, space for each antenna is therefore reduced.
Modern electronic device is also required to integrate many function modules (e.g., dual speakers for stereo audio playback, dual microphones, cameras for capturing 3-dimensional images, high capacity battery, etc) into a compact form factor, and room for each antenna is consequently compromised. In addition, for improved physical robustness and better user experience, modern electronic device tends to adopt metallic housing, which also suppresses area left for antenna since antenna should be apart from metallic part.